Multiple personas
I don't think we are there yet, but I can imagine a future where your phone/tablet are your compute device.
The Operating system will have different personas (this is where windows phone/RT may have a head start)
When undocked the OS (and apps) take on mobile persona all based around touch and non multi tasking work loads.
You then dock at your office/home and a desktop persona comes into play, allowing multiple monitors, multi tasking use of a mouse and keyboard
If you need real grunt a server is only a network cable or cloud away